The present invention relates to apparatus for mixing powder.
More specifically, but not exclusively, the present invention relates to apparatus for mixing powder that is specially adapted to processing radioactive powder, such as plutonium dioxide (PuO2). Such powder mixing apparatus must not only comply with constraints concerning the uniformity, grain size, and isotopic composition of the powder while also ensuring that no segregation occurs, it must also comply with constraints concerning safety and criticality that are inherent to the fissile nature of the radioactive powder.
The powder mixing apparatuses that have been proposed in the past do not enable both of those conditions to be complied with effectively.
To achieve this object, the present invention provides powder mixing apparatus, comprising:
a cylindrical body of circular section and of substantially horizontal longitudinal axis, which body is leakproof and has two disk-shaped walls and one annular wall, said body being provided with at least one filling orifice situated at the top of said body and with at least one emptying orifice opening out into the bottom of said body;
a disk placed coaxially inside said body, the edge of said disk being substantially in contact with the annular wall so as to subdivide said body into two cylindrical compartments of substantially equal volume, said disk being provided on each of its faces with at least one blade that is substantially in contact at least with the disk-shaped wall adjacent to said blade, said blade serving to guide said powder during rotation of said disk to a radially inner end segment of said blade adjacent to a transfer orifice passing through said disk so as to enable at least a portion of the powder to pass from one compartment to the other on each revolution of the disk, said blades being angularly offset;
a horizontal drive shaft secured to the center of said disk to rotate said disk; and
motor means for rotating said drive shaft.
This solution using a bladed disk placed in a cylindrical body and provided with transfer orifices makes it possible to homogenize the powder contained in the cylindrical body in very effective manner by mixing.
When the present invention is used with radioactive powder, it is essential in order to comply with criticality constraints, to make provision for the width of the annular wall of the cylindrical body to be smaller than a value set by safety and criticality constraints. In this way, a xe2x80x9cflatxe2x80x9d type cylindrical body is obtained presenting a circular section that is relatively large relative to its axial or longitudinal dimension.
The mass of powder contained in the powder mixing apparatus must be known, both in order to obtain batches of similar mass and also to restrict said mass so as to obtain good mixing, which is a function of the total volume of the cylindrical body serving as the mixing reservoir.
Another object of the present invention is thus to enable the mass of the cylindrical body that serves as the powder reservoir to be measured continuously, in particular during the filling stage, so as to interrupt powder feed once the proper filling level has been reached.
This object is achieved by the fact that the powder mixing apparatus further comprises a rigid frame and a system, such as a load cell, for weighing the cylindrical body by suspension, the system comprising a deformable element connected to said frame and from which the cylindrical body is suspended. Under such circumstances, it will be understood that variation in the length of the deformable element represents variation in the weight of the cylindrical body, in particular while it is being filled with powder.
Another object of the present invention is to satisfy safety constraints associated with seismic risks so as to provide powder mixing apparatus that presents freedom of movement that is controlled and limited.
To achieve this object, provision is made for the powder mixing apparatus further to comprise an assembly mounted on said frame to guide the cylindrical body in vertical translation. This guide assembly allows the cylindrical body to move in vertical translation to a limited and controlled extent, while strictly limiting the movement of the cylindrical body in all other directions (horizontal movements and rotations).